[Security] MacVim affected by netrw command injection via crafted directory names in NetrwMaps() (vim < 9.2.0481)

[Security] MacVim affected by netrw command injection via crafted directory names in NetrwMaps() (vim < 9.2.0481)

Summary

MacVim bundles the vim source at version 9.2 (patches 1-321 in the current build), which is
below the patched version 9.2.0481 that fixes a command injection vulnerability in the
netrw plugin's s:NetrwMaps() function.

Vulnerability Details

• Upstream fix: vim 9.2.0481 (commit 8e41c34aba0e775d2e3bf6f0e2da1b1c5317f3df)
• Upstream CVE/GHSA: pending (no CVE assigned as of 2026-05-18)
• Affected code: runtime/autoload/netrw.vim — s:NetrwMaps() function
• Vulnerability type: CWE-94 — Improper Control of Generation of Code (Code Injection)

Root Cause

In s:NetrwMaps(), several buffer-local key maps are constructed dynamically using exe
with the current directory path interpolated into the command string:

" runtime/autoload/netrw.vim (macvim r183, lines 4943, 4959-4968)
let mapsafecurdir = escape(b:netrw_curdir, s:netrw_map_escape)
...
exe 'nnoremap <buffer> <silent> <nowait> <del> :call <SID>NetrwLocalRm("'.mapsafecurdir.'")<cr>'
exe 'nnoremap <buffer> <silent> <nowait> D     :call <SID>NetrwLocalRm("'.mapsafecurdir.'")<cr>'
exe 'nnoremap <buffer> <silent> <nowait> R     :call <SID>NetrwLocalRename("'.mapsafecurdir.'")<cr>'

The escape set (s:netrw_map_escape = "<|\n\r\\\<C-V>\") escapes backslash before
< characters, turning them into \<. However, with the B flag set in cpo (the
default), \<CR> in the RHS of a mapping is interpreted as an actual Enter keystroke
rather than the literal two-character sequence \<CR>.

An attacker who can create a directory named with a <CR> (four literal characters
<, C, R, >) followed by Vimscript commands can cause those commands to execute
when the victim opens that directory in netrw and triggers any of the D, R, or
<Del> maps.

Attack Scenario

1. An attacker creates a directory named:

   /path/to/evil<CR>:let g:pwned=1<CR>
   

   (where <CR> represents the four literal characters <, C, R, >)
2. The victim opens this directory in netrw inside MacVim (e.g., via :Explore).
3. s:NetrwMaps() constructs the D map with the path interpolated; escape() turns
   < into \<, yielding \<CR>:let g:pwned=1\<CR> in the RHS.
4. With cpo containing the B flag (default), \<CR> in the map RHS is interpreted
   as actual Enter. The map fires :call NetrwLocalRm("evil, then Enter, then
   :let g:pwned=1, then Enter — executing injected Vimscript.
5. Any user keystroke of D, R, or <Del> while browsing the directory triggers
   the injected commands.

Affected MacVim Code

" netrw.vim line 4943 (macvim r183)
let mapsafecurdir = escape(b:netrw_curdir, s:netrw_map_escape)

The escape() call does not protect against <CR> (four-character angle-bracket
notation) because the B flag in cpo makes the map interpreter expand \<CR> to
actual Enter.

Affected MacVim Version

MacVim r183 (vim 9.2 patches 1-321) — current HEAD as of 2026-05-18.

The fix commit 8e41c34aba0e775d2e3bf6f0e2da1b1c5317f3df from vim/vim is not present
in the macvim-dev/macvim repository:

git log --all --oneline | grep 8e41c34a  # returns no output

Suggested Fix

Merge or cherry-pick vim/vim patches up to at least 9.2.0481:

• Upstream fix: https://github.com/vim/vim/commit/8e41c34aba0e775d2e3bf6f0e2da1b1c5317f3df

The fix adds a save/restore of cpo with B temporarily removed at the start of
s:NetrwMaps(), preventing \<CR> in interpolated paths from being treated as actual
Enter keystrokes:

function s:NetrwMaps(islocal)
    let _cpo = &cpo
    set cpo-=B
    " ... map construction ...
    let &cpo = _cpo
endfunction

References

• Upstream fix commit: https://github.com/vim/vim/commit/8e41c34aba0e775d2e3bf6f0e2da1b1c5317f3df
• Related fix (vim 9.2.0480 / CVE-2026-43961): https://github.com/vim/vim/commit/8af0f098c3a42a28661d0295364e6e0fd7dbc92c

Comienza con runtime/autoload/netrw.vim y la función s:NetrwMaps(), y luego compara el código fuente de Vim incluido con el commit upstream 8e41c34aba0e775d2e3bf6f0e2da1b1c5317f3df. Revisa el historial del repositorio para encontrar el fix que falta e integra el cambio upstream al menos hasta Vim 9.2.0481. La tarea estará terminada cuando MacVim ya no contenga la implementación afectada de netrw.